In some cases n.Add() can reuse the []Word buffer and n.Sub() reallocate it
away. If that happens, we're out of luck with 0.99.0+ versions (since
3945e81857). I'm not sure why it does that, bit
width doesn't change in most of the cases and even if it does, we still have
enough of it in cap() to hold the old Abs() value (when we have a negative
value we in fact decreate its Abs() first and increase it back
afterwards). Still, that's what we have.
So when we have processTokenTransfer() doing Neg/Neg in-place its value is not
affected, but the original []Word bits that are reused by amount value are
(they're shared initially, Amount: *amount).
name old time/op new time/op delta
ToPreallocatedBytes-8 65.8ns ± 2% 45.6ns ± 2% -30.73% (p=0.008 n=5+5)
name old alloc/op new alloc/op delta
ToPreallocatedBytes-8 0.00B 0.00B ~ (all equal)
name old allocs/op new allocs/op delta
ToPreallocatedBytes-8 0.00 0.00 ~ (all equal)
Turns out, it's almost always allocating because we're mostly dealing with
small integers while the buffer size is calculated in 8-byte chunks here, so
preallocated buffer is always insufficient.
name old time/op new time/op delta
ToPreallocatedBytes-8 28.5ns ± 7% 19.7ns ± 5% -30.72% (p=0.000 n=10+10)
name old alloc/op new alloc/op delta
ToPreallocatedBytes-8 16.0B ± 0% 0.0B -100.00% (p=0.000 n=10+10)
name old allocs/op new allocs/op delta
ToPreallocatedBytes-8 1.00 ± 0% 0.00 -100.00% (p=0.000 n=10+10)
Fix StorageItem reuse at the same time. We don't copy when getting values from
the storage, but we don when we're putting them, so buffer reuse could corrupt
old values.
